A conventional membrane switch may comprise a substrate, a separator, and a membrane having a surface which is opposed to the substrate. Circuitry is provided on the substrate including one or more switches, each of which comprises spaced-apart switch electrodes. The membrane has a commoning conductor thereon in opposed relationship to the electrodes so that the membrane can be flexed towards the substrate at the switch site and the switch electrodes will be electrically commoned by the commoning conductor thereby to close the switch. The commoning conductor usually comprises a conductive grid on the membrane extending over an area which encompasses both of the switch electrodes.
In the design of circuits for membrane switches, it is highly desirable to arrange the circuit such that it is not necessary to have the circuit conductors cross over each other. The circuitry on the substrate and on the membrane is commonly applied by a silk screening process using conductive inks and if none of the circuit lines cross each other, all of the circuits, including the conductors and the switch electrodes, can be applied to the substrate in a single silk screening operation.
Under some circumstances, it is impossible to avoid crossovers of conductors because of the arrangement of the conductors and the density or complexity of the circuit. If crossovers are required, it is common practice to provide an isolation layer of insulating material on the conductors of the substrate where the crossover is required. The jumper conductor or crossing conductor is then silk screened or otherwise applied to the surface of the isolation layer.
The use of isolation layers and crossing conductors greatly increases the manufacturing cost of membrane switches for the reason that an additional two steps are introduced into the manufacturing process, the application of the isolation layer and the provision of the crossing conductor on the isolation layer. The present invention is directed to the achievement of improvements to membrane switches which will reduce or eliminate the need for crossovers in circuits where such crossovers have previously been required.
A membrane switch assembly in accordance with the invention is of the type comprising a substrate having first and second switch electrodes thereon which are adjacent to, and electrically isolated from, each other at a switch site, and a membrane which is parallel to and adjacent to, the substrate. The membrane has a commoning conductor thereon at the switch site which is opposed to the first and second switch electrodes. Separator means are provided between the membrane and the substrate and serves to maintain the membrane in spaced relationship to the substrate, the separator means being discontinuous at the switch site so that the membrane can be flexed towards the substrate with resulting contact of both the first and second switch electrodes by the commoning conductor thereby electrically to common the first and second switch electrodes. The membrane switch assembly is characterized in that the substrate has a circuit conductor thereon which extends between the first and second switch electrodes and the commoning conductor comprises first and second commoning pads which are opposed to the first and second switch electrodes respectively, and which are separated from each other by a commoning conductor passageway which is opposed to the circuit conductor. The first and second commoning pads are electrically connected to each other by a bridging conductor on the membrane, the bridging conductor having first and second ends which are connected to the first and second commoning pads and has an intermediate portion which is located beyond the switch site. The intermediate portion extends over a portion of the membrane which is maintained in spaced relationship to the substrate by the separator means whereby upon flexure of the membrane in the vicinity of the switch site towards the substrate, the first and second commoning pads will contact the first and second switch electrodes thereby closing switch at the switch site, and the circuit conductor will not be contacted by the first and second commoning pads.
In accordance with further embodiments, the separator means comprises a separator film having an opening at the switch site and the substrate and the membrane comprise a single sheet of film which is folded along a fold line.